1. Field of the Invention
The present invention relates to electrical distribution systems and, more specifically, to a system for detecting parameters in a busway joint used in an electrical distribution system.
2. Description of the Related Art
Electrical distribution systems within typical buildings (and other structures, such as industrial facilities, power generation facilities and outdoor applications, etc.) rely on a number of different systems to transmit electrical power throughout the building. One type of system used for this purpose includes a power busway for distribution of electrical energy within building and other facilities. A power busway is an engineered product that includes bare or insulated bus conductors (in the form of bars, rounds or tubes) in an overall protective metallic housing. The busway is manufactured in lengths of typically ten feet or less, which are joined together in the field during installation using a bolt-secured busway joint that is secured with one or more joint bolts. The construction details of busway and busway joints vary from manufacturer to manufacturer but one thing remains constant—the bolted busway joint must be properly installed for the busway to achieve its designed operation and service life. Manufacturers have routinely relied on joint bolt torque as the controlling variable for proper installation. However, installing contractors often fail to torque the busway joint bolts properly. Even though some manufacturers have introduced twist-off torque control bolt heads in an attempt assure proper installation, many errors are still made during the installation phase for a number of common reasons and many end-users do not routinely perform adequate preventive maintenance on busway systems.
Notably, a loose busway joint is frequently hard to detect. It will usually not fail during the initial operation or be detected during testing of the busway. In many cases, a completely loose joint can survive for several years prior to catastrophic failure.
Many busway manufacturers and industry groups recommend that joint bolt torque be checked at least annually. A joint bolt torque check can only be performed while the busway is de-energized. Since a busway is likely serving a large part of a building or facility, management is reluctant to de-energize the busway for maintenance causing a multi-hour outage for its tenants or production operations. Many commercial tenants or industrial processes operate 24 hours a day and utilize critical equipment that must not be interrupted. A typical short shutdown may cost a building owner $100 k in direct and indirect costs. Thus, joint bolt torque checks are often foregone.
A loose joint will operate with a higher than normal temperature due to the poor electrical contact in the joint surfaces. Most manufacturers and industry groups now recommend that an infrared (IR) survey be conducted periodically to assess busway system joints. A major advantage of the IR survey is that it can be conducted while the busway is still energized. IR surveys are most common only in the most high end users and critical systems.
Still, IR surveys do not detect all busway joint faults. An IR survey can easily fail to identify a troubled joint if proper procedures are not followed. Also, the survey must be conducted when the busway is under a high electrical load (so that the inadequate joints will overheat to the point of detection). In a large building, a survey usually will be conducted over a full day with the result that some parts of the busway may be surveyed while under less than a high load. Also, an IR survey is usually only conducted no more frequently than once per year (an sometimes as infrequently as every two to four years and in some cases not at all) due to high costs or the failure to perceive a need to perform such surveys. Many problems can develop in a period of months. An incipient problem can develop from IR-undetectable to failure in less than the typical inspection interval.
Therefore, there is a need for a system that monitors busway joints on a real time basis.